Thorn Linear Halogen with Quartz Spine - K/14 100W
The original linear halogen lamps had two limitations, in that it was found to be not possible to produce them in ratings below about 300W, and that they had to be operated horizontally. This was owing to the method of filament support, held by small coils of wire that rest on the inner surface of the quartz tube. Lower wattages require finer diameter filaments, and below a certain point these did not have sufficient strength to carry the support wires. Moreover since the supports are free to slide along the tube, the filament will sag and fail prematurely if operated more than a few degrees from the horizontal.

Both of these problems were solved in a particularly elegant fashion, by Alex Halberstadt of Thorn Lighting in 1979. He was first to conceive the quartz spine construction, in which a narrow diameter quartz cane is sealed into the lamp alongside the filament. This bears a number of looped tungsten wires which support the filament without distorting it, the spine being supported itself by a pair of wires welded to the moly foils in the pinch-seals. This innovation resulted not only in Thorn being first to introduce the 200W, 150W and 100W linear halogen lamps, but also first with this smallest version that introduced the 78.3mm standard.

Another challenge with low current halogen lamps was short life arising from bromine attack of the colder filament tails. Thorn achieved a remarkable 4000 hour life by plugging the ends of the filament tails with a solid tungsten wire where they enter the pinch, to increase their strength. In parallel the halogen chemistry was changed to a novel bromine-iodine mixture to reduce the rate of the halogen cycle - note the feint purple hue of iodine vapour in the detail photo.
Manufacturer: Thorn EMI
Lamp Power: 100 Watts
Lamp Voltage: 240-250 Volts
Lamp Current: 4.41 Amperes
Cap Type: R7s Silver plated contacts
Bulb Type: T-10.5 T-3 in eighths/inch
Bulb Finish: Clear
Filament Type: CC-8 Coiled-Coil Axial
Lighted Length: mm Inches
Atmosphere: Krypton-Halogen CHI3 + PNBr2
Luminous Flux: 1350 lumens
Luminous Efficacy: 13.5 lm/W
Luminous Intensity: N/A
Beam Distribution: N/A
Colour Temperature & CRI: CCT: 2850K Ra: 100
Chromaticity Co-ordinates: CCx: 0.444 CCy: 0.406
Lifetime: 4000 hours
Burning Position: Universal
Insertion Length: 78.3mm 3.08 Inches
Factory: Enfield, London United Kingdom
Date of Manufacture: 1989 April Date Code: 9D
Original Value: GB £5.78 (1988)
References: 1) Thorn Lighting Comprehensive Catalogue, 1989/90 UK, pp.399-400
2) Thorn Lighting Comprehensive Price List, 7th November 1988, p.68
3) GB Patent 2,064,215 - Improvements in Lamp Filament Supports, A.L. Halberstadt, Thorn Lighting Ltd, Filed 1979.